Summary

• Fix incorrect checked state inheritance when pressing Enter at the beginning of a checked checklist item
• Intercept Enter key before BlockNote's handler using runsBefore + keyboardShortcuts
• Perform split with correct states: new line unchecked, original line retains checked state

Problem

When pressing Enter at the text start of a checked ([x]) checklist item:

• New line incorrectly inherited checked state
• Original line lost its checked state

Root Cause

BlockNote's splitBlockTr passes keepProps=undefined to tr.split(), which resets checked to false on the new node via attrs: {}. The original node retains checked: true.

Solution

A new BlockNote extension (checklistSplitFixExtension) intercepts the Enter key before check-list-item-shortcuts using runsBefore. For any checklist item (checked or unchecked) with cursor at content start, it inserts a new unchecked checkListItem block before the current one and moves the cursor there.

Test Plan

• Checked item, Enter at line start → new line unchecked, original stays checked
• Checked item, Enter mid-text → both stay checked (delegated to BlockNote)
• Unchecked item, Enter at line start → new line with cursor (delegated to BlockNote)
• Empty checked item, Enter → converts to paragraph (delegated to BlockNote)
• Checkbox click toggle → no interference
• Undo/Redo → works correctly

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